Magnetic Field Evolution Leading to Solar Flares II. Cases with High Magnetic Shear and Flare-Related Shear Change

Abstract

Abstract Following Paper I in which we considered five solar flares, we have selected another three solar flares greater than GOES X-ray class M/Hα importance 1. The three active regions discussed here are characterized by high magnetic shear. We investigated the spatial relationships among Hα flare ribbons, soft X-ray (SXR) flare loops, and magnetic configurations for the three flares produced in these active regions. Our results show that only one of these three flares satisfies the sufficient conditions for a flare to occur proposed by Hagyard (1990, AAA 052.075.047). We also discuss the magnetic shear changes around the flaring time only along the neutral lines associated with the studied flares and over the whole flaring area. The flare-related changes on the neutral line are small (2°–4°) and the association of these changes with the flares is not conclusive. The average shear in the flaring areas of the flares associated with high shear decreases significantly after the flares and it may be a better parameter to characterize the flare-related shear changes in such cases.